Introduce a new 'json-interpolation' language that extends JSON with
${...} variable interpolation syntax. Features include:
- Monarch tokenizer with nextEmbedded for JavaScript inside ${...}
- Variable context API for custom completion and hover providers
- Diagnostics filtering to ignore errors inside interpolations
- Full JSON language service integration (formatting, symbols, etc.)
- Support for JSONC-style comments and trailing commas
Usage:
```typescript
monaco.languages.jsonInterpolation.jsonInterpolationDefaults.setVariableContext({
getVariables: () => [
{ name: 'env', type: 'string', value: 'production' }
]
});
```
